Spo2 galaxy note 4

I have a very big problem with my galaxy note 4, SM-N910F and the shealth app 4.4.0.0119. Android 5.01.
I can not measure the SPO2 but pulse and UV measuring works. At the first 2 or 3 months it works perfectly but now not because the SPO2 icon isn't there and I cannot reinstall it.
The sensor is O.K. I also done an Complete reset of the Note 4. But no positive result
Please help me.
Thank you very much